Ac power control circuits for reactive power loads

ABSTRACT

AN AC POWER CONTROL CIRCUIT FOR REACTIVE LOADS AND VARIOUS MOTORS INCLUDING A PHASE CONTROL TRIGGER CIRCUIT FOR ACTUATING A POWER CONTROL SWITCH WHEREIN THE TRIGGER CIRCUIT TIMING IMPEDANCE IS VARIED IN ACCORDANCE WITH AN IMPEDANCE VARYING ELEMENT REACTIVE IN A MOTOR FEEDBACK CIRCUIT.

United States Patent inventor Jack B. Harwell Euless, Tex, Appl. 'No.725,247 Filed Apr. 1, I968 Patented June 28, 1971 Assignee ElectronicControl Corporation Enless, Tex.

AC POWER CONTROL IRCUITS FOR REACTIVE POWER LOADS 13 Claims, 5 DrawingFigs. US. Cl. 318/227, 318/230, 318/345 lnt. CL H02p 5/40. Fieldofsearch 318/227, 230, 345

AC MOTOR SPEED CONTROL, HOME APPLIANCE BUILDER, August 1964 (pp. 13 15,38) Primary Examiner0ris L. Rader Assistant Examiner-Gene Z. RubinsonAttorney-Robert C. Peterson ABSTRACT: An AC power control circuitfor-reactive loads and various motors including a phase control triggercircuit for actuating a power control switch wherein the trigger circuittiming impedance is varied in accordance with an impedance varyingelement reactive in a motor feedback circuit.

PATENTEU M28197! 3,588.64?

SHEEI 1 OF 2 FIG.3 #MJW in/4v,

AC POWER CONTROL CIRCUITS FOR REACTIVE POWER LOADS BACKGROUND OF THEINVENTION l. Field of Invention This invention relates to power controlcircuits and more particularly to timing circuits in power controlcircuits wherein a motor feedback circuit controls an impedance varyingelement whereby power is applied to a motor responsive to the motorload. 1

2. Description of the Prior Art Various power control circuits have beendevised in the past using many types of semiconductors and other solidstate devices. Typically the silicon controlled rectifier has beenutilized in such circuits.

Most power control circuits have utilized certain basic concepts. Eachhas a timing circuit for actuating the power control switch to applypower across the load. The timing circuit was essentially an RC circuitusing a variable resistor to change the conduction angle of the powercontrol switch, and consequently, determine the duration of the powercycle. The conduction angle could be varied by changing thepotentiometer resistor setting.

Unfortunately, the prior art failed to provide for an auto maticincrease in power responsive to the load demand in full wave ACcircuits. Thus, whenever the load demand varied the power control switchremained operative to apply load power only during the preset interval.This deficiency remained until the invention described herein.

INVENTION SUMMARY Applicant's invention affords a thertofore unavialablepower control circuit whereby any increase in AC power load provides afeedback responsive to effect and increase in the conduction angle of abilateral solid state power control device and thereby increase theaverage load power. The invention utilizes a feedback circuit whichincludes an impedance varying element or device that reacts to feedbackcurrent to vary the impedance in the timing circuit of the motor speedcontrol. The invention is equally applicable to both universal motorsand induction motors. Likewise, the invention is applicable to any powercontrol system. Typically, the impedance varying element or device(Impedance Element) may be any one of a number of different devices, forexample, any bilateral control device or switch, inverse parallel SCRs,bilateral amplifying devices, and current gain device. Other specificdevices of the aforementioned types are disclosed in the following US.Pat. Nos. 3,317,746; 3,275,909; 3,274,463 and 2,769,926. Moreover, theprimary requirement for the Impedance Element is that its impedancernust vary responsive to feedback, whereupon in a motor control circuitthe conduction angle for the power control switch is advanced orretarded as required to increase or decrease load power.

Moreover, the Impedance Element may be characterized as a reactive oractive element that, under the feedback conditions of current from amotor in a power control circuit, will vary the impedance in the timingcircuit whereby the conduction angle will be advanced or retardedresponsive to the power load to control the load power.

It is therefore an object of the invention to provide a power controlcircuit with a feedback mechanism whereupon the load power mayautomatically be compensated for varying power load;

Another object of the invention is to provide a power control circuitwherein the timing circuit includes an Impedance Element responsive tovariation in power load to advance or retard the conduction angle of thepower control switch to control load power;

Another further object of the invention is to provide a power controlcircuit with feedback means whereupon the speed of the motor may bemaintained at a desired rate regardless of the motor load;

Another further object of the invention is to provide a motor powercontrol circuitwhcrein the timing circuit includes an active ImpedanceElement responsive to a component of motor load power whereby suchImpedance Element effects advancement or retardation of the conductionangle of the motor power control switch;

Another further object of .the invention is to provide a power controlcircuit having power line compensation with a compatible feedbackmechanism whereupon the load power may automatically be compeitsated fornot only power line fluxuations, but also varying power load; and

Another further object of the invention is to provide a motor powercontrol circuit Having power line compensation wherein a compatibletiming circuit includes an Impedance Element responsive to a'componentof motor load power whereby such Impedance Element effects advancementor retardation of the conduction angle of the motor power controlcircuit.

DRAWING DESCRIPTION FIG. I illustrates a simple circuit embodiment ofthe invention as applied to a universal AC-DC motor;

FIG. 2 illustrates a more advanced circuit embodiment of the inventionthan in FIG. 1, again as applied to a universal motor;

FIG. 3 illustrates a typical circuit application of the invention asapplied to an induction motor;

FIG. 4 is a schematic of another circuit application of the invention asapplied to an induction motor; and

FIG. 5 is a schematic of the invention as applied in a circuit havingpower line compensation.

PREFERRED EMBODIMENTS Initially, it will be understood that theinvention is applicable to both the so called universal motor and theinduction motor. The power control circuit for each type motor issomewhat different, however, the inventive concept remains that is motorfeedback is utilized to advance or retard the conduction or firing angleof the power control circuit.

Referring now to the drawings and particularly FIG. 1, the circuitcomprises a pair of terminals 1 and 2 provided on lines 3 and 4,respectively, and may be suitably connected to a volt AC power line. Auniversal motor M is connected on one side to line 3 and is connected onthe other side by line 5 to the anode A of bilateral power controlswitch 0, The cathode K of power switch Q is connected to line 4. Thetiming control for power switch Q comprises potentiometer resistor R inparallel with the series circuit of resistor R and impedance varyingdevice or element (Impedance Element) 0, The Impedance Element Q, asillustrated, is simply a bilateral solid state switch similar to powerswitch Q The anode AE of Impedance Element Q, is connected to one sideof resistor R the cathode KB of Impedance Element Q, is connected toline 3. Resistor R is connected at its fixed end to the juncture of line3, one side of motor M and cathode KB of impedance Element 0,. The wiperarm 7 of resistor R and floating end of resistor R, are connectedtogether and to the other side of resistor R, at the juncture ofresistor R, and one side of timing capacitor c,. The other side ofcapacitor C, is connected to line 4. The juncture of timing capacitor C,and resistor R is coupled to the control electrode G of power switch Qby bilateral trigger diode T.

The control electrode GE of Impedance Element Q, is coupled throughfeedback resistor R to the anode A of power switch Q,. In this mannerresistor R in series with the impedance appearing between controlelectrode GE and cathode KB of Impedance Element Q forms a parallelcircuit with motor M, hence, the voltage across motor M appears acrossthe series circuit of resistor R and the control electrode GE to cathodeKE impedance of Impedance Element In operation. potentiometer resistorR,,, resistor R,, and Impedance Element provides the charging impedanceof timing capacitor C The wiper arm 7 of resistor R, is set for someinitial speed for motor M. As motor M becomes loaded down and tends todecrease in speed, the current change is reflected as an increase incurrent between the control electrode GE and cathode KB of ImpedanceElement Q and as a consequence, the impedance between cathode KB andanode AE decreases. This impedance decrease across Impedance Element Qincreases the charging rate of timing capacitor C, which reaches thefiring voltage to trigger bilateral diode T at a faster rate therebyadvancing the conduction or firing angle of power control switch 0,, andin turn increasing the load power supplied to motor M, consequentlymaintaining the speed thereof. Furthermore, as the motor load decreases,the current between the cathode KE and control electrode GE decreasespermitting the impedance across Impedance Element Q to increase. Thisincrease in impedance across Impedance Element Q decreases the chargingrate of timing capacitor C and consequently, retards the conductionangle of power control switch 0,.

From the foregoing, it will be appreciated that the feedback reactivedevice, Impedance Element Q is in the charging impedance network fortiming capacitor C consequently, the voltage which capacitor C, chargestoward varies depending upon current feedback appearing as a result ofmotor load variations.

The circuit illustrated in FIG. 2 is an actual prototype circuit used tocontrol the power of a universal motor. In more detail, the circuitincludes contact 1 connected to line 3 and contact 2 connected to line 4through a switch 8,. Contacts 1 and 2 provide suitable means to couplethe circuit to a source of AC line power (typically 120 volts, 60cycles). Resistor R, and capacitor C, in series across lines 3 and 4provide a phase shift in the timing circuit. The timing circuit includespotentiometer resistor R having a wiper arm 7 which is ganged withswitch S,. The fixed end of resistor R,, is connected to line 3. Thefloating end of resistor R and wiper arm 7 are connected together. Aresistor R couples the juncture of capacitor C, and resistor R, to thecommon connection of resistor R,,, resistor R, and timing capacitor CThe free end of capacitor C is connected to line 4. The other end ofresistor R,, is connected to the anode AE of Impedance Element 0, (thesame as depicted in FIG. 1 and others). The cathode KB of ImpedanceElement Q is connected to line 3.

The bilateral solid state power switch 0, includes its cathode K, anodeA and control electrode G together with bilateral trigger diode Tconnected to control electrode G, all as a unit. The free end of triggerdiode T is coupled to timing capacitor C, at the common connection withresistor R,The cathode K is connected to line 4, and anode A isconnected to line 5. Line 3 has contact 6 and line 5 has contact 8. Auniversal motor M is coupled'by its contacts 9 and to contacts 6 and 8of lines 3 and 5. Thus, motor M is in the anode A circuit of powerswitch 0,.

The feedback circuit coupling Impedance Element Q, and anode A of powerswitch Q, includes feedback resistor R and matching diode D, in parallelcoupled in series with the parallel combination or resistors R and R(resistors R,, and R may be replaced by a single resistor). Resistor R,and diode D, are connected to anode A of power switch Q, and resistor Rand R,, are coupled to control electrode GE of Impedance Element 01' Thecomponent used in the circuit of FIG. 2 to control the universal motor M(Dayton universal motor, listed in the well known Grainger Cat. No.2Ml44) are listed hereafter:

R, resistor, carbon, 47 K 10 percent watt R, resistor, carbon, 18 K 10percent :5 watt R; potentiometer, carbon, 250 K 30 percent 2 watt Rresistor, carbon 10 K 10 percent A: watt R,, resistor, carbon 5.6 K 10percent 2 watt R,, resistor, carbon 6.8 K 10 percent 2 watt R resistor,carbon, 5.6 K 10 percent 1% watt D, diode, silicon, 200 v. PIV

C, capacitor, paper, 0.1 uf 20 percent 200 v.

C, capacitor, paper, 0.1 uf 20 percent 200 v.

Q, QUADRAC device, 5 amp 200 v. with 43 v. logic device* Q, QUADRACdevice 5 amp 200 V without logic device* S, line switch ganged withpotentiometer R3 *QUADRAC is a trademark of Electronic ControlCorporation and the devices are available as 2003 for Q2 and ZOOST forQ, from the corporation at the address noted 10' hereafter.

The operation of the circuit of FIG. 2 is substantially identical to theoperation of the circuit depicted in FIG. 1. The resistor R, andresistor R and capacitor C, afford a phase shift to sharpen up thetiming of the conduction angle. Resistors R and R,, operate as one. Thediode D, in conjunction with resistor R affords bilateral matching forthe circuit.

Considering FIG. 3, the power control circuit of the invention foroperation with an induction motor will be described. A pair of contacts1 and 2, suitable for coupling the circuit to an AC power line source,are connected to lines 3 and 4 of the circuit. A series circuit ofcurrent protection resistor R,, potentiometer resistor R and timingcapacitor C is connected between lines 3 and 4. Wiper arm '7 of resistorR is connected to the common juncture of resistor R,, and resistor R,,.A series circuit of resistor R,, and the impedance appearing betweenanode AE and cathode KB of Impedance Element Q is connnected betweenresistor R and line 4. A matching resistor R,,, shunts the seriescircuit of resistor R,, and Impedance Element Q Impedance Element Q, hasa control electrode GE which is coupled by feedback resistors R to line5. An induction motor IM is connected onto the circuit between line 4and line 5, thus the induction motor IM is in a parallel circuit withthe cathode KE to control electrode GE of Impedance Element Q, andresistor R,,. The bilateral solid state power switch Q, is connected atits anode A directly to line 3. The cathode K of power switch Q, isconnected directly to line 5, hence, the juncture of resistor R andinduction motor IM. The control electrode G of power switch Q, iscoupled to timing capacitor C by bilateral trigger diode T.

In the induction motor circuit of the invention, the Impedance Element(reactive feedback element) is in parallelcircuit relation to the timingcapacitor and consequently current in the timing capacitor branch of theparallel circuit varies depending on the impedance, hence, current inthe Impedance Element branch of the parallel circuit. a

As depicted in FIG. 3, the operation of the induction motor IM controlcircuit is quite similar to that of the universal motor M circuits ofFIGS. 1 and 2, but with several differences. The induction motor IM isin the cathode circuit rather than in the anode circuit, hence, theImpedance Ele ment Q, is in parallel with the timing capacitor ratherthan in the charging impedance network. It will be observed that theresidual voltage across the induction motor IM provides the desiredfeedback to vary the impedance across the Impedance Element 0;.

Considering FIG. 4, the circuit depicted was actually utilized tocontrol an induction motor. The circuit includes a pair of contacts 1and 2, suitable for coupling the circuit to a source of AC line power,are connected to lines 3 and 4, respectively. The anode A of a bilateralsolid state power control switch Q, is connected directly to line 3. Aninduction motor IM is connected between line 4 and the cathode K ofpower switch Q, by line 5. A series phase shift circuit, comprisingresistor R, .connected to line 3 and in series with capacitor C,, isconnected to the anode AE of Impedance Element Q The cathode KB ofImpedance Element Q, is coupled to the juncture of line '5 and motor IM.The control element GE of Impedance Element Q, is connected through theparallel circuit of resistor R andmatch ing diode D, in series withfeedback resistor R, to the juncture of line 4 and motor IM.

The timing capacitor C is connected to line 5 and'through potentiometerresistor R by current protecting resistor R to sistor R connects thephase shift network to the juncture of resistor R and capacitor C Thetiming capacitor C is coupled by bilateral trigger diode T to thecontrol electrode G of power switch 0,.

Considering the operation of the power control circuit of FIG. 4, itwill be observed that again the Impedance Element Q, is in parallelcircuit relation with timing capacitor C and consequently, current inthe timing capacitor branch of the parallel circuit varies depending onimpedance, hence, current in the Impedance Element branch of theparallel circuit.

The components used in the circuit of FIG 4 to control induction motorIM (Nutone Model AK4K36A, 115 v., 60 cycle, [.1 amps) are listedhereafter: I R resistor, carbon, 27 K percent watt R, resistor, carbon,10 K 10 percent 2% watt R potentiometer, carbon, 250 K 30 percent 2 wattR resistor, carbon, 8 K 10 percent /2 watt R resistor, carbon, 3.4 K 10percent 5 watt R resistor, carbon, 3 K 10 percent Va watt C capacitor,paper 0.1 uf percent 200 v. C capacitor, paper 0.1 uf 20 percent 200 v.D diode, silicon, 200 V. PIV v.

T diode, logic device part of Q Q QUADRAC device, 5 amp 200 v. with 43v. logic device* Q QUADRAC device. 5 amp 200 V* *QUADRAC is a trademarkof Electronic Control Corporation and the devices are available as 2003for Q and 2005T for Q from the corporation at the address noted iqrsa tn Referring now to FIG. 5, thecircuit therein depicts the inventionutilized in conjunction with automatic AC power line compensation. Thecircuit includes contacts 1 and 2, for

' coupling the circuit to a suitable source of AC line power,

connected to lines 3 and 4, respectively. The bilateral solid statepower control switch Q, is connected to line 4 at cathode K of the powerswitch 0,. Anode A of power switch O is connected by line 5 to one sideof universal motor M, the other side of motor M being connected to line3. The AC power line compensation in the circuit is afforded by theseries circuits of resistor R connected to line 5 and negative impedancedevice 2,, connected to line 4. The device Z may be any of the well knowbilateral trigger diodes such as .are generally used to trigger gatedpower control switches which are sometimes referred to as break backtrigger diodes.'The negative impedance device 2,, suitable forapplication in this circuit may be obtained, from among others, byordering a line compensating negative impedance trigger diode fromElectronic Control Corporation, Euless, Texas, 76039. The timingcapacitor C is connected to line 4 and through potentiometer resistorR5, to the juncture of resistor R and negative impedance device Z Wiperarm 7 of resistor R is connected to the common connection of resistor Rand capacitor C The feedback Impedance Element Q is connected at thecathode KE thereof to line 3 and anode AE of Impedance Element Q iscoupled to the juncture of timing capacitor C and resistor R, byresistor R The juncture of line 5 and motor M is connected to thecontrol electrode CvE of Impedance Element Q be feedback resistor RTiming capacitor C is coupled to the control electrode G of power switchQ, by bilateral trigger diode T.

In operation of the circuit depicted in FIG. 5, with line voltage highthe negative impedance device 25 effects a slower charging rate ofcapacitor C and with line voltage low the device Z effects a fastercharging rate of capacitor C In this manner the average load powerremains constant regardless of high or low power line voltage. Wheneverthe motor load increases or decreases, the change is reflected in thefeedback as an impedance change across Impedance Element 0:.Consequently, since Impedance Element Q affords part of the siliconcontrolled rectifiers or transistor means charging path impedance fortiming capacitor C the charging rate of timing capacitor C increases ordecreases thereby effecting an advancement or retardation of theconduction angle of power switch 0,.

Considering the foregoing, it will be appreciated that the feedbackImpedance Element is either part of the charging impedance for thetiming capacitor of the universal motor power control circuits, or inparallel circuit relation with the timing capacitor of induction motorpower control circuits; consequently, the universal motor is in theanode circuit and the induction motor is in the cathode circuit of thepower control switch as herein described.

From the foregoing it will be appreciated that various ImpedanceElements are available and various embodiments of the invention willbecome readily apparent, and all such suggested and apparent changes andmodifications are within the scope of the invention which is limitedonly as necessitated by the scope of the appended claims.

I claim: 1. An AC power control circuit for a reactive power loadcomprising:

a. a power control switch having a pair of power electrodes and acontrol electrode, b. a reactive 'power load in series with saidelectrodes, c. a feedback impedance means, and d. a timing circuit forsaid power control switch in parallel circuit relation with saidreactive power load and pair of power electrodes, said timing circuitincluding;

i. an Impedance Element having at least a portion thereof in series withsaid feedback impedance'means and in parallel circuit relation with saidreactive power load exhibiting impedance variations inversely responsiveto apparent impedance changes of said reactive power load, and

ii. timing means coupled to said control electrode to activate saidpower control switch with advancement or retardation of the conductionangle thereof according to the impedance changes of said lmpedanceElernent.

4 2. The circuit of claim 1 wherein said Impedance Element comprises abilateral semiconductor switch or parallel inverse pair of power device.

3. The circuit of claim 1 wherein said Impedance Element comprisesabilateral semiconductor switch and said power control switch comprises abilateral semiconductor power switch. v V

4. An AC power control circuit for a reactive impedance load comprising:

a. A power control switch having a pair of power electrodes and acontrol electrode,

b. a reactive impedance load coupled in series with the power electrodesof said power control switch,

c. an Impedance Element,

d. a timing circuit, including said Impedance Element, for

said power control switch coupled in parallel circuit relation with thereactive impedance load and power switch for controlling the conductionangle of the power control switch, and

e. feedback impedance means coupling said reactive impedance load intosaid timing circuit in parallel circuit relation with at least a portionof said Impedance Element whereby changes in said reactive impedanceload inversely effects advancement or retardation of the conductionangle.

5. The circuit of claim 4 wherein said timing circuit includes aselectible resistance network,a capacitive reactance network, saidcapacitive reactance network coupled to the control electrode of saidpower control switch, a negative impe'dance'device in parallel circuitrelation with said capacitive reactance network to compensate saidtiming circuit for AC power line variations, and said reactive impedanceload is a motor.

6. The circuit of claim 5 wherein said motor is a universal or currentgain motor and said Impedance Element is in series circuit relation tionwith the reactive impedance load and power control switch forcontrolling the conduction angle of the power control switch, I

e; a feedback impedance means in series circuit relation with at least aportion of said Impedance Element,

f. said feedback impedance means and said at least a portion of saidImpedance Element coupled in shunt circuit relation with said reactiveimpedance load whereby said Impedance Element exhibits impedance changesinversely responsive to changes in said reactive impedance loadeffecting correlative advancement or retardation of theconduction angleof the power control switch. 9. An AC power control circuit for areactive power load comprising:

a. a power control switch having a pair of power electrodes and acontrol electrode,

b. a reactive power load in series with said pair of power electrodes, k

c. a feedback impedance means, and

d. a timing circuit for said power control switch in parallel circuitrelation withsaid reactive power load and pair of power electrodes, saidtiming circuit having; i. a charging impedance means including,

A. an Impedance Element, at least a portion of said Impedance Elementbeing in series with said feedback impedance means,

B. said at least a portion of said Impedance Element and said feedbackimpedance means in shunt circuit relation with said reactive power load,and

C. said charging impedance means exhibiting impedance variationsinversely responsive to apparent impedance changes of said reactivepower load, and

ii. timing means coupled to said control electrode to activate saidpower control switch with conduction angle advancement or retardationcorrelative with impedance changes of said charging impedance means.

10. comprises a universal motor.

11. The circuit of claim 10 wherein said Impedance Element is in seriescircuit relation with said timing means.

12. The circuit of claim 9 wherein said reactive power load comprises aninduction motor.

13. The circuit of claim 12 wherein said Impedance Element is inparallel circuit relation with said timing means.

The circuit of claim 9 wherein said reactive power load

